Aromatic carbonate resins are well known thermoplastic materials which due to their many advantageous physical and mechanical properties find use as thermoplastic engineering materials. The aromatic carbonates exhibit, for example, excellent properties of toughness, flexibility, and high heat distortion temperatures. The aromatic carbonates and methods for their preparation are disclosed, inter alia, in U.S. Pat. Nos. 2,964,974, 2,999,835, 3,169,121, 3,028,365, 3,334,154, 3,275,601 and 3,915,926.
However, these aromatic carbonates generally suffer from low critical thickness values, i.e., the thickness at which a discontinuity in Izod impact values occurs. These low critical thickness values tend to limit wall thickness of molded articles to a thickness below the critical thickness. The aromatic carbonate resins exhibit notched Izod impact values which are dependent on the thickness of the resin article. Thus, for example, while typical notched Izod impact values of one-eighth inch thick polycarbonate test specimens are generally in the range of about 16 foot pounds per inch, typical notched Izod impact values for a one-fourth inch thick polycarbonate test specimen are generally in the range of about 2 foot pounds per inch. The relatively high Izod values of the one-eighth inch thick polycarbonate test specimens are due to the fact that these specimens are thinner than the critical thickness of the polymer and, therefor, upon impact a hinged or ductile break occurs. The low Izod impact values of the one-fourth inch thick polycarbonate test specimens are due to the fact that these specimens exceed the critical thickness of the polymer and, therefore, upon impact a clean or brittle break occurs.
It is well known in the art, and amply described in the patent literature, that the impact properties of aromatic carbonate polymers can be improved by blending an impact modifier with these aromatic carbonate resins. These impact modifiers include the polacrylates, polyolefins such as linear low density polyethylene, rubbery dienic resins such as ethylene propylene diene terpolymers, and styrenic resins. However, in order to significantly improve the impact properties of aromatic carbonate resins these impact modifiers must be present in relatively large amounts, e.g. typically at least about 4 weight percent based on the amount of impact modifier and aromatic carbonate resin.
It would thus be very advantageous if aromatic carbonate resin compositions could be provided which, while exhibiting substantially equivalent impact properties to those obtained using these relatively high loadings of conventional impact modifiers, did so utilizing lower concentrations of these impact modifiers. It is, therefore, an object of the instant invention to provide such aromatic carbonate resin compositions.